A symptom that is often attributed to rhabdomyolysis but has other causes is an exaggerated upward flexion of the hind limb. A regular to irregular hyperflexion of the hind leg when the leg is moving forward without other symptoms is likely to be a neurological condition called stringhalt. Horses with a primary history of abnormal flexing upward of the hindlimb accompanied by a spastic shivering are likely to be sufferng from "shivers"....more about stringhalt and shivers.

The classic symptom of a acutely tied up horse is stiffness: a reluctance to move and when walking taking short hesitant steps while the horse displays an anxious expression. This can vary from a mild stiffness to immobility and when very painful sweating, parking out as if to urinate or other colic-like symptoms. Muscle fasiculations resembling trembling may occur. This might be accompanied by painful hard pelvic and thigh muscles on palpation. The history and signalment of the case will help with the diagnosis.

Sporadic tying up episodes occur most often in horses that are exercised to a level above their level of conditioning. Too rapid acceleration of the training program, resuming training following a idle period , or endurance competitions on hot, humid days all may elicit sporadic tying up because of high body temperatures, loss of fluid and electrolytes in sweat, and depletion of muscle energy stores. These imbalances lead to dysfunction of the cells of the muscle, damage, and possibly cell death. Recent respiratory infections, particularly influenza can exacerbate the problem so horses should not be vigorously exercised during and following a month or two following such infections.

Recurrent Acute Episodes in Young Nervous Horses

Recurrent rhabdomyolysis occurs most often in Thoroughbreds, Standardbreds, and Arabians. Often the problem is seen in nervous individuals during times of stress such as shows, events, and traveling. Mares and Stallions are more often effected and often early in or just prior to exercise. Changing management to provide horses with a calm environment and training schedule and substitution of fat for grains in high caloric rations are helpful means to manage this condition. Exertional rhabdomyolysis continues to be a performance-limiting or career-ending disorder for many equine athletes. As many as 10% of 2 to 3 year old TB's at the track can be effected with 15% of those effected to the point of interfering with training. Recently a hereditary disease has been postulated with the finding of an increased incidence in certain lines of horses. RER appears to be a disorder of intracellular calcium regulation that is triggered by excitement.

Chronic Rhabdomyolysis and Shivers

Chronic forms of tying up are most often horses pocessing an inherited defect in energy (glucose) metabolism. These diseases have been labeled PolySaccharide Storage Myopathy (PSSM) and/or Equine Polysaccharide Storage Myopathy (EPSM). As a result the current common nomenclature is somewhat confusing. It is important to remember that there are a number of different diseases that present with similar symptoms. This is because that though the actual defect in energy metabolism is different they all interfere with energy metabolism in the muscle cell. Often the breed effected may be the best first indicator of the specific defect as these diseases are inherited.

One form effects Quarter Horses and the related breeds like Appaloosas and Paints. Occasionally a similar form has been reported in Morgans and Warmbloods. These are usually calm, well fleshed horses over 2 years of age, though occasionally seen earlier. Besides varying degrees of the chronic symptoms, acute exacerbations have been brought on by changes in housing, management, or exercise level. Recent advances in identifying the specific genetic disorders divides QH's into two groups: a milder labeled Type 1 PSSM and a more severe form of Type 1 that is complicated by a secondary genetic defect. This severe form is characterized by ongoing persistent muscle pain between acute exacerbations and has a poorer prognosis, for more see PSSM below.

Draft breeds suffer from Type 1 PSSM and other forms of PSSM. The incidence is high in draft breeds with the incidence ranging from 25 To 40% of the Belgian and Percheron population. Yes you should read that at least 25% of these horses suffer in varying degrees from this disorder. In one alternate form of PSSM muscle enzymes are sometimes but not always present in elevated levels but the horse suffers from chronic muscle wasting. Others forms are seen as the well described "Monday Morning Disease" where work horses with the weekend off tie-up when worked is resumed. Some have proposed one form of PSSM should be labelled as EPSM in individuals which respond to dietary management alone while PSSM drafts require both nutritional and exercise management for successful treatment.